1. Field of the Invention
This invention relates generally to the field of control circuitry, and, more particularly, this invention relates to in-rush control circuitry which utilizes a fixed resistor and programmable timers to sequentially turn on a first relay, a power factor correction circuit (PFC) and a DC/DC converter.
2. Background of the Invention
When a large power supply is connected to an AC line voltage supply, a short-duration, high amplitude, input current (known as inrush current), results as an internal power supply capacitance is absorbing energy. The inrush current may be many times the steady state current until the power supply reaches equilibrium, i.e., the transient effect continues until the voltage across the internal power supply capacitance reaches a voltage approximately equal to the peak amplitude of the AC line voltage supply.
If a series resistance is used to limit the inrush current, this same resistance will result in power losses during normal operation of the power supply. The duration of the inrush current is extended in In-Flight Entertainment Systems (IFES), because of the large amount of internal capacitance required to hold up the power supply during momentary power interruptions. This long duration, high amplitude inrush current could cause tripping of the AC line circuit breaker or induce line transients that might affect other equipment sharing the common AC power source. A system requirement for IFES necessitates that the inrush current must be limited to less than four times the peak normal operating current which would require a large value of current limiting impedance.
Inrush control circuitry which addresses each of the above set out problems is described below.